This invention relates to the inspection of pipeline, and more particularly to the inspection of pipeline for leaks.
The invention relates to inspection apparatus commonly referred to as inspection pigs which are adapted to travel through and inspect buried pipelines which transmit petroleum products and other fluids. These inspection pigs provide information regarding the presence of pipeline leaks which can lead to explosions that may destroy property and take human lives without the necessity for the expensive operation of unearthing the pipeline.
Inspection pigs typically are propelled through a pipeline by the pressure of fluids therein and travel through a pipeline without substantially disrupting its operation. These pigs usually comprise a plurality of annular cups which engage the inner wall of the pipeline against which pipeline fluids act to propel the pig. The inspection of pipeline by pigs which measure the pressure differential between a test chamber defined by the flexible annular cups and a region in the pipeline outside the test chamber is old and well known in the prior art. For example, see U.S. Pat. Nos. 3,782,172 to McCarron (1974), 3,817,086 to Dorgebray (1974), 3,016,733 to Dean et al. (1962), and 3,196,686 to Cole (1965).
One problem which arises in many of the prior art pigs is that when the flexible cups pass over obstructions in the pipeline, such as welds, pressure changes and fluid flows are experienced which may be interpreted erroneously as caused by leaks.
A second problem with prior art devices has been that substantial changes in the pipeline diameter such as those caused by dents, have tended to cause pressure differentials and fluid flows which have been interpreted as leaks.
Another problem in the prior art has been that small flows of fluid through passages in the pig which are normal during the inspection process but not caused by leaks have made recognizing true pipeline leaks more difficult.